1. Field of the Invention
The present invention relates to a magnetic tape unit for performing read/write of data on a magnetic tape.
2. Description of the Related Art
In recent years, a magnetic tape unit using a magnetic tape as a storage medium has been developed and put into practical use as an external storage device for a computer. In a read/write operation of the magnetic tape unit, the magnetic tape is traveled in contact with the magnetic head. In waiting for a read/write process, the magnetic tape is kept in contact with the magnetic head. Accordingly, if such a waiting condition continues for a long time, there is a possibility that the magnetic tape may adhere to the magnetic head; so, the measures for solving this problem have been desired. In a particular case that an air escaping groove is formed on a magnetic tape contact surface of the magnetic head, so as to make a good contact between the magnetic tape and the magnetic head, there is a possibility that the shape of this air escaping groove may be transferred to the magnetic tape to make the surface of the magnetic tape uneven, causing an error in the read/write operation.
One of the conventional methods for preventing the adhesion of the magnetic tape to the magnetic head or preventing the transfer of the groove shape to the magnetic tape is to provide a gap at a central portion of the magnetic head and blow air against the magnetic tape from this gap with an air pump, thereby avoiding the contact between the magnetic tape and the magnetic head. Another conventional method is to perform a reciprocating motion of the magnetic tape by a small distance during a rest period where the read/write operation of the magnetic head is not performed (Japanese Patent Publication No. 57-8533).
In the former method, the air pump, which is expensive and large, is required to avoid the contact between the magnetic tape and the magnetic head, causing a difficulty of reduction in size and cost of the magnetic tape unit. In the latter method, the short-distance reciprocating motion of the magnetic tape is performed usually with a predetermined period, which is set to a constant value irrespective of temperatures in the magnetic tape unit. Accordingly, the following disadvantage occurs. In general, the higher the temperature, the more the adhesion of the magnetic tape to the magnetic head tends to occur. However, if the period of the reciprocating motion is set to a unduly short period in spite of low temperatures, the magnetic tape may be damaged by the reciprocating motion, whereas if the period is set to a long period in spite of high temperatures, the adhesion of the magnetic tape to the magnetic head cannot be prevented.